This invention relates generally to techniques of electronically filtering a desired signal from undesired noise, and more specifically relates to linear digital filters.
A matched digital filter is basically a linear filter whose transfer function has been matched in some way to a particular electronic signal or environment in order to perform a filtering that is optimum for some particular purpose. The filter is particularly matched to a signal plus noise input from which the signal is desired to be extracted. A goal in the use of such filters is to accept a part of the incoming signal plus noise that is most representative of the signal contained therein.
One type of digital filter which has been used is a Fast Fourier Transform (FFT) digital filter. This type of filter suffers from a disadvantage of a large number of components which make it large and expensive. Prior digital filters, both the Fast Fourier Transform and others, have included means to manually adjust their transfer function but no provision has been made for continuously adapting the filter to a changing noise and signal environment.
Therefore, it is an object of the present invention to provide a method and apparatus of filtering electronic signals that is simple and less expensive than types presently employed.
It is an additional object of the present invention to provide a method and apparatus for filtering electronic signals that automatically adapts its transfer function to changing noise conditions.